1. Field of Invention
The present invention relates generally to special effect generators for video signals and, more particularly, relates to a video special effect generator of simple arrangement and which can be manufactured inexpensively.
2. Description of the Background
A video special effect generator has been proposed by which an original video image can be rotated, enlarged, shrunk and moved on a picture screen of a television monitor in a three-dimensional (3D) fashion.
In accordance with this previously proposed video special effect generator, an original video image 11 shown on the left-hand side in FIG. 1 is converted into digital data, and stored in a frame memory (not shown). In accordance with processing of the original video image, for example image rotation processing, the read address of the frame memory, that is, the address in the frame memory corresponding to the display address on the display screen is calculated in a real-time fashion, and the original video image data is read out from the frame memory in accordance with the read address resulting from the calculation. Thereafter, the video image data read out from the frame memory is converted into analog form and displayed on the display screen, so that a rotation-processed video image 12 is displayed on a display screen 13 as shown in at the right-hand side in FIG. 1.
In the prior art video special effect generator, in order to display the original video image 11 that is processed to be rotated in a three-dimensional manner, address calculations must be performed to determine the location of coordinates of the display screen 13 relative to the coordinates of the rotation-processed video image.
Thereafter, if the image to be displayed on the display screen 13 involves a portion smaller than the original video image 11, that is, a shrunken image, then the calculation of the coordinates of the location of the rotated image becomes very difficult. For example, assuming that a point .alpha. of the original video image 11 represents an origin, then a point .beta. on the display screen 13 is a negative value relative to the processed video image 12, and a point .gamma. on the display screen 13 is a much larger value. Thus, the coordinate system of the whole display screen 13 has a large dynamic range. Therefore, in order to calculate all of the coordinates of the display screen 13 in real time fashion, it is necessary to use a very complicated and expensive calculating circuit.